In a U.S. Pat. No. 4,185,191, issued Jan. 22, 1980 to Norman L. Stauffer and assigned to the assignee of the present invention, a range determination system is shown which is useable in a through-the-lens camera for positioning the taking lens at a desired correct focus position with respect to a remote object within the field of view. That system utilizes a plurality of small detectors such as charge coupled devices (CCD) or charge injection devices (CID) mounted in an array to receive radiation from the scene being viewed. The detectors are arranged in pairs with each pair being mounted behind a small lenslet so that each pair receives a view of the exit pupil of the taking lens but one of the detectors in each pair receives radiation primarily from a first portion of the taking lens while the other of the detectors in each pair receives radiation primarily from a different portion of the taking lens. The result is to create two similar curves indicative of the radiation distribution pattern from the scene being viewed. At the proper focus position, the two curves coincide, but as the object changes position with respect to the camera, the two curves move with respect to each other to indicate an out-of-focus situation. The two curves move with respect to each other in a first direction when the object is closer to the camera than the desired focus position and move in an opposite direction with respect to each other as the object moves further from the camera than the desired focus position. By determining the direction of movement of the two curves with respect to each other, it is therefore possible to determine the direction that the taking lens has to be moved to achieve the desired focus position.
In a copending application of Norman L. Stauffer and Dennis J. Wilwerding, Ser. No. 16,595, now U.S. Pat. No. 4,249,073 and assigned to the assignee of the present invention, an improvement on the above-mentioned U.S. Pat. No. 4,185,191 was disclosed wherein a method and apparatus for determining the direction in which the two similar curves need to be moved in order to produce the coincidence indicative of a proper focus position is described. In that application, a value indicative of the slope of the curves at predetermined points is obtained and this value is multiplied by the difference in the value of the output of the detectors at such points. The product is summed over a predetermined range. The summation value is substantially zero when the two curves coincide but will have a characteristic such as plus or minus to indicate the direction the taking lens must be moved when the two curves do not coincide.
In a copending application of James D. Joseph and Dennis J. Wilwerding, Ser. No. 58,964, filed July 20, 1979, now U.S. Pat. No. 4,250,376 and assigned to the assignee of the present invention, a further improvement was disclosed which eliminated the need for obtaining a product and in lieu thereof operates to (1) produce a first signal representative of the absolute magnitude of the difference between the outputs of two detectors, one from each of the curves, (2) produce a second signal indicative of the absolute magnitude of the difference between the outputs of two other detectors, one from each of the curves, and (3) subtract the two signals and then sum the result over a predetermined range. The resultant summation value, as in the case of the above-mentioned copending application, Ser. No. 16,595, is substantially zero when the two curves coincide, will have a first characteristic such as a negative sign when the two curves are displaced in the first direction and a second characteristic such as a positive sign when the two curves are displaced in the opposite direction.
While the above patents and applications describe circuitry that is satisfactory to determine the direction in which the taking lens must be moved in order to achieve a proper focus position, it does not produce a signal which can be used to determine the amount of movement that taking lens has to be moved from its present position in order to arrive at the proper focus position. Knowing both the direction of movement and the amount of movement necessary to achieve a proper focus position has a number of advantages including the ability to operate the taking lens in a proportional manner, that is, to move the taking lens very rapidly to a position near the proper focus position and thereafter slowing the taking lens movement down so that it approaches the exact focus position without overshoot or oscillation. Such a system may also be used to provide the photographer with an indication of the amount the taking lens is presently out-of-focus which information may be more useful to a photographer than merely knowing the direction the taking lens needs to be moved.